Method of refining metals



United SatoPw 3,001,865 METHOD OF REFINING METALS Karl J. Korpi, Pasadena, Calif., and Raymond C. Johnson, Orwigsburg, pany, New York, N.Y., a corporation of Delaware Filed June 23, 1958, Ser. No. 743,734 7 Claims. (Cl. 75-841) This invention relates to the production of high melting point metallic elements and has for an object the provision of an improved method or process for producing high-purity refractory metals. More particularly, A

the invention contemplates the provision of an improved method or process for producing high-purity,'high melting point metallic elements, including titanium, zirconium, hafnium, vanadium and uranium, by the disproportionation of lower iodides of such elements. This application is a continuation-in-part of our copending application Serial Number 543,514, filed October 28, 1955,v

now abandoned, and entitled Method of Refining Metals.

Pa., assignors to The Lummus Come r' lcg 3,001,865

these metals "result from their high melting point. The

property of titanium, in the molten state, of acting as a Titanium, zirconium, hafnium, vanadium and uranium have become important commercial materials in view of the unusual properties which they exhibit. At present, there are several Ways of recovering such metals all of which are complicated and expensive. For instance, the procedures now used for the manufacture of titanium are the following:

(1) Reduction of titanium tetrachloride or other titanium tetrahalide with either sodium or magnesiumwith subsequent elimination of the sodium or magnesium halide which is formed by washing or distillation.

(2) Reduction of titanium oxide with calcium hydride at elevated temperature. This procedure has not been too successful since the product is always heavily contaminated with oxygen.

(3) Thermal dissociation of a titanium tetrahalide on a hot filament under vacuum. J

(4) Electrolytic recovery from fusedsalts. T At the present time, the most widely usedcommercial method is the reduction of titanium tetrachloride with" magnesium or sodium followed by' subsequent distillation of the magnesium chloride or sodium chloride byproduct in a vacuum. This process, popularly referred to as the Kroll process, is inherently expensive since it produces a titanium halide from a titanous oreand then reduces the halide with another substantially pure metal. In such a process, the necessary expense of the pure secondary metal establishes a very high minimum cost. Also the titanium is formed as a metallic sponge which necessitates further processing to obtain the metal in a useable form. a

As indicated, titanium, as well as'the other aforementioned metals, have many unusual physical and chemi-- cal properties. In order to be workable and generally useful, these metals have to .be supplied in an extraordinarily pure form. Smallpercentages of oxygen, nitrogen, hydrocarbon or carbon embrittle the metal markedly so that it cannot be handled by conventional metal working procedures. Under these conditions, great-care is taken to eliminate these undesirable elements from being present while the metal is being formed. While the above noted processes are illustrativeof titanium rewater, and even react with nitrogen from the air to form nitrides of the metal. a u

Other difliculties with the treatment and recovery or nearly universal solvent presents a major problem in handling the metal in such a state. Almost all 'of the impurities tolerable in other materials reduce the ductility of the high melting point metals to the degree of being unworkable.

To illustrate our process of producing high purity, high melting point, metallic elements we have hereinafter described our invention with regard to the treatment and recovery of titanium.

'In accordance with the present invention, the metal titanium is produced as a relatively high purity product of the little known reactionof titanium monoxide with the titanium halides. 7 Although the reactions of decom position of sub-halides to metal. and higher halides has been known, the possibilities of combined titanium halide reactions have 'not been appreciated. Through our invention pure ductile titanium is produced in plate or ingot form, rather than in oxidizable crystals or sponge form, and at a cost substantially below that of present day methods. Further, our invention provides a relatively low temperature process which can operate at substantially atmospheric pressure with a minimum of heat input and without the need for hydrogen or other costly reducing materials such as sodium'ormagnesium. Other objects and advantages of our invention will appear from the following description of one form of embodiment taken in connection with the attached drawing which is a simplified flow. diagram of the reaction according to the invention.

than a limitation as to a specific metal or type of appara- Accordingly, in our method, titanium bearing ores such as rutile, ilmenite and titarn'te or titanium dioxide-bearing slag obtained as a result of the'smelting of titaniferous iron ore, are charged to pulverizer 10. These ores or slag, even in their purest state, contain iron, silicon and aluminum as regular impurities. Alkaline earth metals, such as calcium, are likewise commonly found in various titaniarich ores. We reduce the titanium dioxide of such ores with powdered cabon suppliedto pulverizer 12 and produce titanium contaminated with lower oxides nium, we prefer to employ petroleum coke or charcoal.

The carbon in the mixture serves primarily to remove the oxygen from the titanium dioxide in the form of carbon monoxide and carbon dioxide, thereby reducing the titanium dioxide to titanium. Some of the carbon may react with the titanium dioxide to form titanium carbide and carbon monoxide and carbon dioxide. To prepare. titanium in furnace 14, wefhave used a mixture of parts by weight of crushed rutile and 27 parts by.

weight of crushed petroleum coke, consolidated by pressure to a dense solid. Analysis of the rutile and petroleum' coke used by us indicated the following:

Rutile: Percent TiO 93.20 F e O 1.73 810; 2.03 2 3 0.70 CaO 1.74 2 5 D60 Patented Sept. 26, 1961 3 Petroleum coke: Percent Volatile matter 8.81 Fixed carbon 89.86 Ash 1.33

The furnace 14 may be an electric resistance furnace or it may be of any typical arc, cupola or fluidized design. In the furnace, the titanium dioxide is reduced by carbon by a series of step-wise reactions to produce lower oxides of titanium, elemental titanium, and titanium carbide in accordance with the following chemical equations:

(becomes favorable about 2000-2100 C.)

A mixed product of TiO and TiC may be obtained in furnace 14 by carrying out the reaction at a temperature of 900-1100 C. In presence of excess carbon, titanium carbide will be the favored product near 1000" C. at atmospheric pressure according to Reaction 3. However, it is desired to make the maximum of metal and a minimum of carbide and lower oxides, hence the furnace must be heated to from lS-2100 C. with the proper carbon ratio to promote Reactions 2 and 5. The carbon monoxide and dioxide formed during reduction is driven off under suitable conditions through line 16.

Products of the furnace other than carbon monoxide and carbon dioxide are cooled to about 700 C. and are in the form of a fused agglomerate containing titanium, titanium carbide and titanium monoxide plus impurities such as small amounts of iron, chromium, vanadium and silicon. This material is ground or pulverized in pulverizer 18 for further handling.

The pulverized titanium-titanium monoxide mixture is then charged to reactor 20, which is operated under conditions to exclude oxygen, nitrogen and moisture. This reactor is preferably maintained at a temperature of between 625 C. and 1025 C. and at substantially atmospheric pressure. Under the conditions of elevated temperature and controlled atmosphere, the pulverized crude titanium mixture introduced to the reactor is subjected to the action of a higher metal iodide vapor (MX entering through line 22 so that an exothermic reaction results. The reaction in reactor 20 is exothermic in nature that only enough heat to start up needed from an external source. The temperature within the reactor is controlled by the amount of halide vapor input through line 22.

We have found that any of the halides which readily combine with titanium may be used to form the halide vapor entering reactor 20 through line 22. Principally we have formed metallic titanium according to our process using iodine, as the combined halogen present in the higher metallic halides (MX and the lower metallic halide (MX For the purpose of general explanation, the metal and halide portions of all compounds illustrated in the drawing are represented by the symbols M and X, respectively with h and l designating the higher and lower halide form, respectively.

The vapor in line 22 is principally a higher halide of titanium (MX but in some cases may include equilibrium amounts of lower halides and upon reaction with the titanium mixture charged to reactor 20 forms a liquid lower halide of titanium (MX'J which is removed through line 24.

The titanium higher halides function somewhat in the manner of caifiers accordance with specific reactions illustrated by the following equations:

The titanium oxides and carbide present in the re actor charge that do not react with the higher halides under the' aforementioned conditions, remain behind in the reactor as impurities. Depending upon the relative densities of the varied impurities and the particular lower halide formed in the process, these impurities will either sink or float. Those that float can be skimmed off the top of the liquid lower halide through line 26, while those that sink can be removed from the bottom as sludge through line 28. The lower halide formed can be removed from near the middle of the liquid layer through line 24.

The impurities of line 28, comprising mainly titanium carbide and titanium monoxide, can be introduced into an auxiliary reactor (not shown) for further reaction to produce lower halides of titanium according to the following equations:

Both of these reactions are favorable at temperatures below about 500 0.; hence such auxiliary reactor should be operated at about 400 C. while the tetrahalide vapor is introduced. This reactor should be operated batchwise so that after charging and reacting the solid titanium carbide and titanium monoxide with the tetrahalide vapor, such reactor is then heated to the melting point of the dihalide of titanium. Under these conditions, the trihalide disproportionates to dihalide and tetrahalide and the liquid dihalide may thereafter flow to reactor 30 to join the flow of liquid dihalide in line 24. The tetrahalide vapors may remain in the auxiliary reactor to react with a fresh charge of titanium carbide and ti: tanium monoxide at the lower temperatures with additional tetrahalide added as required.

The lower liquid halide (MX removed from reactor 20 through line 24 is then charged to a second reactor 30 which contains a plurality of electric heating elements generally indicated at 32. Each heating element is enclosed in a metal (M) sheath 34 and is maintained at a temperature of from 800 C. to 1500 C. The liquid pool of lower halide within reactor. 30 is heated by the sheathed heaters to an average temperature of between 625 C. and 1025 C. and in this temperature range, the lower metallic halide is'thermally disproportionated to form the metal, which deposits on the sheaths or collectors in a high state of purity, and to higher metallic h id (MXn)- I The decomposition of titanium dihalide to yield metallic titanium is according to the following equation: (10) 2T X :-.T1+T1X,

( qu l (5 Any titanium trihalide which may be present is genenally unstable and dissociates into titanium dihalide and titanium tetrahalide. The tetrahalide and some of the unreacted dihalide formed during the thermal disproportionation in reactor 30 is in a gaseous state and is removed through line 36 and pumped by pump 38 to condenser 40. In condenser 40, the gaseous mixture is cooled to a point whereby any titanium dihalide is condensed for return to reactor 30 in line 42 while the gaseous titanium tetrahalide is recirculated to line 22 through line 44 and provides substantially all of the tetrahalide requirement of reactor 20.

t s the n tial art n 11 9 29 rrqqes' he halid and is; re cti g wi h ti anium u qsss in wat nuq s circulation between reactors 20 and 30. Qniy a small 2mm of e highe al de (M rl i as mak up since the halide circuit is substantially closed with only small amounts of halide loss through the formation of volatile halides of the metallic impurities in the raw material. The volatile halides are removed through line 46 to condenser 48 where the higher halide is condensed and returned through line 46 to reactor 20. The volatile halides are then removed from the system through line 50.

Within the reactor 30 there is a continuous deposition and growth of metal on the heater sheaths 34 whereby they obtain the form of an ingot. Periodically the sheaths are removed and form the pure metal product, after which a new sheath is placed over the heating element and returned to the liquid pool of lower metallic halide.

Around each heater sheath is a refractory thermal barrier 52 which acts to substantially shield the liquid pool of lower halide from the higher temperature of the heater while at the same time directs the liquid halide in recirculating flow past the sheath for disproportionation.

In some instances the heating elements may also be maintained in the vapor phase over the liquid in reactor 30 as for example where it is found that the particular lower halide used disproportionates more rapidly as a vapor.

To illustrate a preferred embodiment of our process, operating conditions for the deposition of high purity titanium, are set forth in the following example.

Example Vaporous titanium tetraiodide (Til at a temperature in the neighborhood of 380 C. reacts rapidly with crushed slag (comprised of lower titanium oxides, titanium, titanium carbide and small amounts of impurities) in a bed maintained at a temperature in the neighborhood of 650 C. at atmospheric pressure to form liquid titanium diiodide, the diiodide forming a liquid pool at a point removed from the slag bed. The liquid titanium diiodide, maintained at a temperature in the neighborhood of 750 C. at atmospheric pressure, disproportionates to titanium and titanium tetraiodide vapor in the presence of a heated titanium sheath (950 C.) immersed within the pool. The titanium tetraiodide vapor is continuously withdrawn from the space above the pool and recirculated for use as the slag halogenating media. Analysis of the titanium coating on the titanium sheath shows only slight porosity and the presence of only trace impurities.

Having now described our invention with regard to the production of elemental titanium, zirconium, hafnium, vanadium and uranium and having given an example of a preferred embodiment of our process using titanium as the exemplified product, we desire a broad interpretation of the invention within the scope of the disclosure herein and the following claims.

We claim:

1. The method of producing a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium and uranium by the disproportionation of a lower iodide of the metal to form the metal and a higher iodide of the metal which comprises: halogenating a crude mixture of said metal with a higher iodide of said metal. to form a lower iodide of said metal; efi'ecting said halo genation in a first reaction zone at substantially atmospheric pressure and at a temperature above the melting point and below the boiling point of said lower iodide of the metal and above the boiling point of said higher iodide of the metal thereby to form said lower iodide of said metal in said zone; withdrawing said lower iodide as a liquid from said first reaction zone and introducing it into a second reaction zone for disproportionation therein to said metal and a higher iodide of said metal; efiecting said disproportionation in said second zone at substantially atmospheric pressure in the presence of a heated body of said metal by forming a pool consisting primarily of said lower iodide around said body and maintaining the liquid in said pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature sufiicientto maintain said pool'temperature; depositing a substantially solid layer of disproportionated metal on said body; and recirculating the higher iodide formed during dispropora tionation to said first reaction zone to provide the higher iodide utilized for said halogenation.

2. The method of producing a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium and uranium by the disproportionation of a lower iodide of the metalto form the metal and a higher iodide of the metal which comprises: halogenating a crude mixture of said metal with a higher iodide of said metal to form a lower iodide of said metal; effecting said halo-W genation in a first reaction zone at substantially atmospheric pressure and at a temperature above the melting point and below the boiling point of said lower iodide of the metal and above the boiling point of said higher iodide of the metal thereby to form said lower iodide of said metal in said zone; withdrawing said lower iodideas' a liquid from said first reaction zone and introducing it into a second reaction zone for disproportionation therein to said metal and a higher iodide of said metal; eifect'mg said disproportionation in said second zone at substantially atmospheric pressure in the presence of a heated body of said metal by forming a pool consisting primarily of said lower iodide around said body and maintaining the liquid in said pool at a temperature above the melting point and below the boiling point of said lower iodide by and a higher iodide oftitanium which comprises:"halo-' genating a crude mixture of titanium with a higher iodide of titanium, to form a lower iodide of titanium; eifecting said halogenation in a first reaction zone and at a temperature above the melting point and below the boiling point of said lower iodide of titanium and above the boiling point of said higher iodide of titanium thereby to form said lower iodide of, titanium in said zone; withdrawing said lower iodide as. a liquid from said first reaction zone and introducing it into a second reaction zone for disproportionation therein to. titanium and a higher iodide of titanium; effecting said disproportionation in said second zone in the presence of a heated body of titanium by forming a pool of said lower iodide around said body and maintaining the liquid in said pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature sufficient to maintain said pool temperature; depositing a substantially solid layer of disproportionated titanium on said body; and recirculating the higher iodide formed during disproportionation to said first reaction zone to provide the higher iodide utilized for said halogenation.

4. The method of producing zirconium by the disproportionation of a lower iodide of zirconium to form zirconium and a higher iodide of zirconium which comprises: halog'enating a crude mixture of zirconium with a higher iodide of zironium to form a lower iodide of zirconium; efiecting said halogenation in a first reaction zone and at a temperature above the melting point and below the boiling point of said lower iodide of zirconium and above the boiling point of said higher iodide of zirconium thereby to form said lower iodide of zirconium in said zone; withdrawing said lower iodide as a liquid from said first reaction zone and introducing it into a second reaction zone for disproportionation therein to zirconium and a higher iodide of zirconium; eifecting said disproportionation in said second zone in the presence of a heated body of zirconium by forming a pool of said lower iodide around said body and maintaining the liquid in said pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature sufiicient to maintain said pool temperature; depositing a substantially solid layer of dispro'portionated zirconium on said body; and recirculating the higher iodide formed during disproportionation to said first reaction zone to provide the higher iodide utilized for said halogenation.

5. The method of producing hafnium by the disproportionation of a lower iodide of hafnium to form hafnium and a higher iodide of hafnium which comprises: halogenating a crude mixture of hafnium with a higher iodide of hafnium to form a lower iodide of hafnium; effecting said halogenation in a first reaction zone and at a temperature above the melting point and below the boiling point of said lower iodide of hafnium and above the boiling point of said higher iodide of hafnium thereby to form said lower iodide of hafnium in said zone; withdrawing said lower iodide as a liquid from said first reaction zone and introducing it into a second reaction zone for disproportionation therein to hafnium and a higher iodide of halfnium; etfecting said disproportionation in said second zone in the presence of a heated body of hafnium by forming a pool of said lower iodide around said body and maintaining the liquid in said pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature sufiicient to maintain said pool temperature; depositing a substantially solid layer of disproportionated hafnium on said body; and recirculating the higher iodide formed during disproportionation to said first reaction zone to provide the higher iodide utilized for said halogenation.

6. The method of producing vanadium by the disproportionation of a lower iodide of vanadium to form vanadium and a higher iodide of vanadium which comprises: halogenating a crude mixture of vanadium with a higher iodide of vanadium to form a lower iodide of vanadium; effecting said halogenation in a first reaction zone and at a temperature above the melting point and below the boiling point of said lower iodide of vanadium and above the boiling point of said higher iodide of vanadium thereby to form said lower iodide of vanadium in said zone; withdrawing said lower iodide as a liquid from said first 'reaction'zone and introducing it into a sec ond reaction zone for disproportionation therein to v'anadium and a higher iodide of vanadium; eifecting' said disproportionation in said second zone in the presence of a heated body of vanadium by forming a pool of said lower iodide around said body and maintaining the liquid in said pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated to a temperature suflicient to maintain said pool temperature; depositing a substantially solid layer of disproportionated vanadium on said body; and recirculating the higher iodide formed during disproportionation to said first reaction zone to provide the higher iodide utilized for said halogenation. V

7. The method of producing uranium by the disproportionation of a lower iodide of uranium to form uranium and a higher iodide of uranium which comprises: halogenating a crude mixture of uranium with a higheriodide of uranium to form a lower iodide of uranium; elfecting said halogenation in a first reaction zone and at a temperature above the melting point and below the boiling point of said lower iodide of uranium and above the boiling point of said higher iodide of uranium thereby to form said lower iodide of uranium in said zone; withdrawing said lower iodide as a liquid from said first reaction zone and introducing it into a second reaction zone for disproportionation therein to uranium and a higher iodide of uranium; eiiecting said disproportionation in said second zone in the presence of a heated body of uranium by forming a pool of said lower iodide around said body and maintaining the liquid in. said pool at a temperature above the melting point and below the boiling point of said lower iodide, said body being heated .to a temperature sufficient to maintain said pool temperature; depositing a substantially solid layer of disproportionated uranium on said body; and recirculating the higher iodide formed during disproportionation to said first reaction zone to provide the higher iodide utilized for said halogenation.

References Cited in the file of this patent UNITED STATES PATENTS 2,556,763 Maddex June 12, 1951 2,670,270 Jordan Feb. 23, 1954 2,706,153 Glasser Apr. 12, 1955 2,785,973 Gross Mar. 19, 1957 2,890,952 Korpi et al. June 16, 1959 

1. THE METHOD OF PRODUCING A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM, HAFNIUM, VANADIUM AND URANIUM BY THE DISPROPORTIONATION OF A LOWER IODIDE OF THE METAL TO FORM THE METAL AND A HIGHER IODIDE OF THE METAL WHICH COMPRISES: HALOGENATING A CRUDE MIXTURE OF SAID METAL WITH A HIGHER IODIDE OF SAID METAL TO FORM A LOWER IODIDE OF SAID METAL, EFFECTING SAID HALOGENATION IN A FIRST REACTION ZONE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE AND AT A TEMPERATURE ABOVE THE MELTING POINT AND BELOW THE BOILING POINT OF SAID LOWER IODIDE OF THE METAL AND ABOVE THE BOILING POINT OF SAID HIGHER IODIDE OF THE METAL THEREBY TO FORM SAID LOWER IODIDE OF SAID METAL IN SAID ZONE, WITHDRAWING SAID LOWER IODIDE AS A LIQUID FROM SAID FIRST REACTION ZONE AND INTRODUCING IT INTO A SECOND REACTION ZONE FOR DISPROPORTIONATION THEREIN TO SAID METAL AND A HIGHER IODIDE OF SAID METAL, EFFECTING SAID DISPROPORTIONATION IN SAID SECOND ZONE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE IN THE PRESENCE OF A HEATED BODY OF SAID METAL BY FORMING A POOL CONSISTING PRIMARILY OF SAID LOWER IODIDE AROUND SAID BODY AND MAINTAINING 